The cockerel, generally, develops an upright stance, thicker, longer legs, and strutting, knot knee walk. The cockerels will normally develop their secondary sex characteristics of red wattles and red combs weeks and weeks before the females. This is true virtually across the board.
As for becoming mean, a rooster isn't necessarily mean. He has a genetic, biological job to do and that is alert, defend and mate. His behaviors are normal for him. That said, some roosters, because of indiscriminate breeding, are indeed nasty and should be put down and not used for breeding, it is that simple.
The hormones kick in for cockerel around week 15. Still, one must judge a cockerel who matures into a rooster, over a period of time.
